"On December 8, 2005, we published a story that wondered: Firefox 1.5: Not Ready For Prime Time? In response, some 450 (and climbing) InternetWeek, InformationWeek, TechWeb Pipelines, and Scot's Newsletter readers have sent details about their experiences with Firefox 1.5. A picture is emerging about Firefox 1.5 in the real world - on a small percentage of Windows, Mac, and Linux computers - that is less than positive."

I had some of these problems listed, but with firefox 1.0, not 1.5. Like all of a sudden it would crash when visiting a yahoo page or some page with flash. Or after quitting I had to manually quit the firefox.exe process before using firefox again. That problem was caused by java applets.
Well after upgrading to 1.5, the 2nd problem is gone. But I still saw a couple of crashes due to the flash plugin. So I disabled it and no longer saw crashes. I reinstalled it from scratch and haven't seen a crash so far.

>Like all of a sudden it would crash when visiting a yahoo page or some page with flash.

I have a hunch that most of reported problems with high memory usage are due to stupid flash ads. Animated gif, java are also obvious suspects. I use Flashblock, it's a must. I also turn off Java, and animations--Prefbar extension is great for that. Never had any problems, crashes happen, but only after hours of really heavy use.